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High Performance 3D Scanning System
The Navy has identified a crucial need to inspect surfaces submarine
propellers. These propellers are as large as 35 ft. in diameter.
Submarine propellers are currently being fabricated at Naval Foundry and
Propeller Center (NFPC) in Philadelphia. Submarine propellers require
sophisticated geometry to support very accurate data models required to
create digital programs for computer based machines.
This proposed solution is based on Accordion Fringe Interferometry (AFI).
AFI is one of the most promising non-contact technologies to emerge for
large scale applications. Invented at MIT Lincoln Laboratory in 1999,
AFI employs laser light from two point sources to illuminate an object
with an interference fringe pattern. A CCD camera is used to record the
curvature of the fringes from a viewpoint offset from the projector by
about 30 degrees. The degree of apparent curvature coupled with the
known angle between the camera and laser source enables the AFI
algorithm to digitize the surface of the object being measured. The
chief advantages of AFI over conventional structured light techniques
are that AFI has nearly infinite depth of field; it projects very
bright, accurate patterns easily distinguished from background light;
and AFI admits simple and less expensive solid state designs. A key
element will be the development of technology to overcome reflections.
Filleted areas of the propeller are complex enough that light may be
reflected off, two or more, surfaces before reaching the camera. This
situation is called multi-path, and is a serious problem for optical
systems resulting in erroneous measurements. Various optical and
algorithmic strategies for mitigating the deleterious effect of
multi-path will be investigated. A data model is constructed by creating
a cloud of points representing the surface of the object being measured.
NCMS Program Manager: Bill Waddell, (231)264-9774,
wwadd49648@aol.com
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